The saddest thing about Lioness: Hidden Treasures, the first posthumous release from Amy Winehouse, is that it's merely a perfectly enjoyable, lovingly compiled collection of odds and ends. And it only intermittently hints at the tortured-soul complexity that made the doomed British singer such a compelling - and sometimes great - artist.

That's because Winehouse, whose alcohol-poisoning death in July was tragically unsurprising, never conceived of Lioness (Universal Republic ***) as the follow-up to Back to Black, her 2006, five-Grammy-winning second album.

According to producer Salaam Remi, who worked on Lioness along with fellow knob-twiddler Mark Ronson, Winehouse did finish writing a sequel to Back to Black, the album that spawned both her defiantly destructive signature song, "Rehab," and the excellently existential hit "You Know I'm No Good."

She never got around to recording it, however. There are rumors that Winehouse cut a reggae album in 2009 that was rejected by her record label, which saw it as a dangerously noncommercial change of direction. And last month, Remi told reporters that at the time of her death Winehouse was planning to form a supergroup of sorts with British saxophonist and rapper Soweto Kinch and ubiquitous Roots drummer Ahmir "?uestlove" Thompson.

But all signs indicate that when Winehouse died, she did not leave behind an enormous trove of unreleased recordings, a la Tupac Shakur. Instead, as with Kurt Cobain, there appear to be a smattering of songs, some from an earlier, innocent, and not yet artistically mature period, along with a precious few others that tantalizingly hint at what might have been.

In the former category are a handful of covers, such as a reggae-flavored take on the Ruby & the Romantics' "Our Day Will Come" and a Wall-of-Sound buildup of Gerry Goffin and Carole King's "Will You Still Love Me Tomorrow?" There's an undeniable sweetness to those songs, and to a scat-singing cover of "The Girl From Ipanema." They date as far back as 2002, preceding Winehouse's debut album, Frank, which came out the following year.

Those covers don't plumb the depths as thoroughly as the modernized and melancholic updated girl-group musings that made Back to Black so powerful, though they do convey the creeping sense of dread that came naturally to the Billie Holiday-influenced singer.

That sense of looming darkness is more pronounced on such Lioness cuts as the moody blue "Half Time," a woozy jazz ballad that features ?uestlove on drums. It also hovers over "Like Smoke," with a haunting Winehouse chorus, that was finished posthumously with a pair of jarring verses, complete with Occupy Wall Street references, from Nas, Winehouse's friend and maybe boyfriend who's said to be the subject of Back to Black's "Me and Mr. Jones." (The new song includes Nas' cringe-inducing rhyme "Why did God take away the homie?" and "I'm a firm believer that we all meet up in eternity.")

It's also there on Lioness' two Back to Black alternative versions, a slowed-down. string-decorated "Tears Dry" and a stripped-down demo of "Wake Up Alone." The latter, in particular, serves as a reminder that along with being a coolly confident, warmly emotive singer, skilled at slurring syllables to maximize a lyric's mystery, Winehouse was a sharp, self-analytic writer.

That may have been lost on anyone who knew Winehouse through tabloid coverage of her often-sordid public and private life, rather than her music. But it can be heard anew on Lioness' stunning, depressive, and more-heartbreaking-than-ever "Wake Up Alone": "I stay up, clean the house, at least I'm not drinking / run around, just so I don't have to think about thinking / That silent sense of content that everyone gets, just disappears as soon as the sun sets."

Contact music critic Dan DeLuca at 215-854-5628, deluca@phillynews.com, or @delucadan on Twitter. Read his blog, "In the Mix," at www.philly.com/inthemix.